This invention relates generally to the control of a hydrostatic transmission and more specifically to the apparatus for the control of the variable displacement hydraulic pump of the hydrostatic transmission.
It is well known in the art to control the displacement of a variable displacement pump by controlling a source of pressurized fluid being directed to the displacement controller thereof. In these known systems, the displacement controller is controlled strictly by the pressure being directed thereto in response to operator movement of an input lever. The output speed and torque is normally proportional to the degree of movement of the input lever. In machines having attachments that are being operated independently of the hydrostatic transmission, the forward or reverse movement of the machine during the time that the independent attachment is being used many times causes the independent attachment to not perform in the proper manner. For example, the independent attachment may be forced away or up from its normal intended path due to the forces induced thereon by the forward or reverse movement of the machine being to great or the work tool may stall. It is desirable to have a system that permits the operator to remotely control the pressure in the hydrostatic loop without the use of special tooling while performing required tasks with the machine.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a control arrangement is provided for use in a fluid system having a power source drivingly connected to a hydrostatic system, a fluid driven work implement, and a source of pressurized pilot fluid, the hydrostatic system having a variable displacement pump, a fluid motor fluidity connected to the variable displacement pump and operative to provide output power to an output. The variable displacement pump has a displacement controller thereon to control the displacement of the variable displacement pump. The control arrangement includes a pilot control arrangement connected to the source of pressurized pilot fluid and operatively connected to the displacement controller of the variable displacement pump. An adjustable relief valve is provided in the control arrangement and is operatively connected to the pilot control arrangement to control the level of pilot pressure being directed to the displacement controller in response to one of the pressure of the fluid between the variable displacement pump and the fluid motor and the pressure of the fluid in the fluid driven work implement.